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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="math_toolkit.fpclass"></a><a class="link" href="fpclass.html" title="Floating-Point Classification: Infinities and NaNs">Floating-Point Classification: Infinities
    and NaNs</a>
</h2></div></div></div>
<h5>
<a name="math_toolkit.fpclass.h0"></a>
      <span class="phrase"><a name="math_toolkit.fpclass.synopsis"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.synopsis">Synopsis</a>
    </h5>
<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">FP_ZERO</span>        <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_NORMAL</span>      <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_INFINITE</span>    <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_NAN</span>         <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_SUBNORMAL</span>   <span class="comment">/* implementation specific value */</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">int</span> <span class="identifier">fpclassify</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isfinite</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">z</span><span class="special">);</span> <span class="comment">// Neither infinity nor NaN.</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isinf</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span> <span class="comment">// Infinity (+ or -).</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isnan</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span> <span class="comment">// NaN.</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isnormal</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span> <span class="comment">// isfinite and not denormalised.</span>

<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">\</span><span class="identifier">math</span><span class="special">\</span><span class="identifier">special_functions</span><span class="special">\</span><span class="identifier">fpclassify</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
      to use these functions.
    </p>
<h5>
<a name="math_toolkit.fpclass.h1"></a>
      <span class="phrase"><a name="math_toolkit.fpclass.description"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.description">Description</a>
    </h5>
<p>
      These functions provide the same functionality as the macros with the same
      name in C99, indeed if the C99 macros are available, then these functions are
      implemented in terms of them, otherwise they rely on <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special">&lt;&gt;</span></code> to function.
    </p>
<p>
      Note that the definition of these functions <span class="emphasis"><em>does not suppress the
      definition of these names as macros by math.h</em></span> on those platforms
      that already provide these as macros. That mean that the following have differing
      meanings:
    </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">;</span>

<span class="comment">// This might call a global macro if defined,</span>
<span class="comment">// but might not work if the type of z is unsupported</span>
<span class="comment">// by the std lib macro:</span>
<span class="identifier">isnan</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">//</span>
<span class="comment">// This calls the Boost version</span>
<span class="comment">// (found via the "using namespace boost::math" declaration)</span>
<span class="comment">// it works for any type that has numeric_limits support for type z:</span>
<span class="special">(</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">//</span>
<span class="comment">// As above but with explicit namespace qualification.</span>
<span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">//</span>
<span class="comment">// This will cause a compiler error if isnan is a native macro:</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">isnan</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">// So always use instead:</span>
<span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">//</span>
<span class="comment">// You can also add a using statement,</span>
<span class="comment">// globally to a .cpp file, or to a local function in a .hpp file.</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">isnan</span><span class="special">;</span>
<span class="comment">// so you can write the shorter and less cluttered</span>
<span class="special">(</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">)</span>
<span class="comment">// But, as above, if isnan is a native macro, this causes a compiler error,</span>
<span class="comment">// because the macro always 'gets' the name first, unless enclosed in () brackets.</span>
</pre>
<p>
      Detailed descriptions for each of these functions follows:
    </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">int</span> <span class="identifier">fpclassify</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
      Returns an integer value that classifies the value <span class="emphasis"><em>t</em></span>:
    </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
              <p>
                fpclassify value
              </p>
            </th>
<th>
              <p>
                class of t.
              </p>
            </th>
</tr></thead>
<tbody>
<tr>
<td>
              <p>
                FP_ZERO
              </p>
            </td>
<td>
              <p>
                If <span class="emphasis"><em>t</em></span> is zero.
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                FP_NORMAL
              </p>
            </td>
<td>
              <p>
                If <span class="emphasis"><em>t</em></span> is a non-zero, non-denormalised finite
                value.
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                FP_INFINITE
              </p>
            </td>
<td>
              <p>
                If <span class="emphasis"><em>t</em></span> is plus or minus infinity.
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                FP_NAN
              </p>
            </td>
<td>
              <p>
                If <span class="emphasis"><em>t</em></span> is a NaN.
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                FP_SUBNORMAL
              </p>
            </td>
<td>
              <p>
                If <span class="emphasis"><em>t</em></span> is a denormalised number.
              </p>
            </td>
</tr>
</tbody>
</table></div>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isfinite</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">z</span><span class="special">);</span>
</pre>
<p>
      Returns true only if <span class="emphasis"><em>z</em></span> is not an infinity or a NaN.
    </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isinf</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
      Returns true only if <span class="emphasis"><em>z</em></span> is plus or minus infinity.
    </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isnan</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
      Returns true only if <span class="emphasis"><em>z</em></span> is a <a href="http://en.wikipedia.org/wiki/NaN" target="_top">NaN</a>.
    </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">isnormal</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
      Returns true only if <span class="emphasis"><em>z</em></span> is a normal number (not zero, infinite,
      NaN, or denormalised).
    </p>
<h6>
<a name="math_toolkit.fpclass.h2"></a>
      <span class="phrase"><a name="math_toolkit.fpclass.floating_point_format"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.floating_point_format">Floating-point
      format</a>
    </h6>
<p>
      If you wish to find details of the floating-point format for any particular
      processor, there is a program
    </p>
<p>
      <a href="../../../example/inspect_fp.cpp" target="_top">inspect_fp.cpp</a>
    </p>
<p>
      by Johan Rade which can be used to print out the processor type, endianness,
      and detailed bit layout of a selection of floating-point values, including
      infinity and NaNs.
    </p>
</div>
<div class="copyright-footer">Copyright © 2006-2021 Nikhar Agrawal, Anton Bikineev, Matthew Borland,
      Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert Holin, Bruno
      Lalande, John Maddock, Evan Miller, Jeremy Murphy, Matthew Pulver, Johan Råde,
      Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg, Daryle
      Walker and Xiaogang Zhang<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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